In the past, L-valine and L-leucine have been produced by a method of fermentation primarily using a microorganism belonging to the genus Brevibacterium, Corynebacterium or Serratia or a mutant thereof which produces L-valine or L-leucine (Amino acid fermentation, JAPAN SCIENTIFIC SOCIETY'S PRESS, pp.397-422, 1986). Although the conventional methods have considerably enhanced the productivity of these amino acids, the development of a more efficient, cost-effective technique is required in order to meet increasing demand for L-valine and L-leucine in the future.
On the other hand, a microorganism belonging to the genus Escherichia is potentially utilized as a potent L-valine or L-leucine-producing microorganism due to its rapid growth rate, progress in genetic analysis and plentiful genetic materials. However, there are few reports documenting the production of these amino acids with from Escherichia microorganisms, and as for L-branched chain amino acids, only a few reports deal with the production of L-isoleucine (Japanese Patent Application Laid-Open No. 5-304969(1993) and Japanese Patent Application Laid-Open No. 5-130882(1993).